A cross profile is a cross section of a river's valley and channel. A - as the river flows downhill there is an increase in vertical erosion. The channel is shallow and narrow because there is not a lot of water in the channel.
What is the load of the river in the cross profile?
Cross profiles Cross profiles of a river Near the source of a river there is more vertical erosion as the river flows downhill, using its energy to overcome friction (A). As a result, the channels...
What is the difference between a river cross profile and channel cross-profile?
· The cross profile of a river changes as it moves from the upper to lower course as a result of changes in the river’s energy and the processes that the river carries out. In the upper course, the valley and channel are narrow and deep as a result of the large amount of vertical erosion and little lateral erosion. The sides of a river’s valley in the upper course are very steep …
What does the long profile of a river represent?
Cross profile A cross profile is a view of the valley from one side to another. A - as the river flows downhill there is an increase in vertical erosion. The channel is shallow and narrow because...
How does river profile change along the course of a river?
· The cross-valley profile is the cross-section through the river valley at any given point along the long profile. It includes the top of one side of the valley, across the valley floor …
What is the cross profile of a river?
Cross profiles of a river. Near the source of a river there is more vertical erosion as the river flows downhill, using its energy to overcome friction (A). As a result, the channels are narrow and shallow and may contain large boulders and angular fragments eroded and weathered from the steep valley sides.
How does a river change shape?
A river changes shape as it flows from its source to its mouth. The shape of the long river profile and the cross river profile changes.
Why does the flow of water increase as the river approaches the mouth?
As the river approaches the mouth, velocity and energy increase due to increased discharge. The river performs more lateral erosion making the channel wider, and smoother (B) and (C). As a result there is less turbulence and friction, making the flow of water more efficient.
Why does the cross profile of a river change?
The cross profile of a river changes as it moves from the upper to lower course as a result of changes in the river’s energy and the processes that the river carries out. In the upper course, the valley and channel are narrow and deep as a result of the large amount of vertical erosion and little lateral erosion.
What are the stages of a river?
The course a river takes is split into three stages, the upper, middle and lower stage . In the upper stage, the river is close to its source and high above its base level (the lowest point the river can erode to1). In the lower stage the river is far away from its source, close to the mouth and not far above its base level.
How does a river erode?
In the upper course, the river has a lot of gravitational potential energy so it has a lot of energy to erode vertically. The bed of the river is eroded greatly while the banks aren’t eroded as much. The river mainly transports large pieces of angular rock and does so by traction because it doesn’t have enough kinetic energy to move the load in any other way. This increases erosion of the bed by corrasion as a result of the load being dragged along the bed of the river. Vertical erosion is further increased by the rough nature of the channel in the upper course which increases the water’s turbulence and its ability to erode. Erosion and transportation only takes place in large quantities in the upper course when the river’s discharge is high after periods of heavy precipitation. When the river’s discharge falls the river stops transporting the large boulders its transporting and deposits them.
What happens to the river's potential energy when it reaches its lower stage?
By the time the river reaches its lower stage, it has next to no gravitational potential energy but lots of kinetic energy resulting in a high velocity.
What happens to the flow velocity of a river?
The average flow velocity of a river increases along its long profile. This makes sense; along the profile, more potential energy is converted to kinetic energy, increasing the velocity. This is only the average velocity however; a cross-section of a river shows that the velocity varies from one side to the other.
Why is erosion lateral?
There isn’t much erosion though because the channel is smoother resulting in less turbulent flow. The main place where erosion takes place is where the river meanders. The average particle size is very small now, another reason for the reduction in erosion. The river’s load is mainly composed of silts and clays and it is transported in suspension or even solution. Like in the middle course, when the river floods it deposits its load but deposition now also takes place at the mouth of the river where the river meets the sea or a stationary body of water.
Why does the valley increase in width?
In the middle course, the valley has increased in width due to the increase in lateral erosion but its depth hasn’t changed significantly because vertical erosion has slowed down. Similarly, the channel’s width has increased but it’s still roughly the same depth. The land to either side of the channel in the valley is now the river’s floodplain and the valley’s sides are much more gentle.
Why is the river channel shallow and narrow?
A - as the river flows downhill there is an increase in vertical erosion. The channel is shallow and narrow because there is not a lot of water in the channel.
What does a long profile show?
A long profile shows how the river changes over its course from its source (where it starts) to its mouth (where it meets the sea).
What are the three things that occur in a river?
Erosion, transportation and deposition all occur in a river. Moving from the upper course to the lower course, the rates of erosion, transportation and deposition change.
How does a river's cross valley profile change?
Rivers in the middle and lower course are characterised by an increase in discharge and this gives the water the (kinetic) energy to erode the riverbed and banks further. There is an excess of energy available due to more efficient usage (channel bed roughness is reduced so less energy is absorbed overcoming friction) and this is used by the river to erode laterally, producing a much wider valley bottom with side slopes which are well separated. In addition, with the decrease in gradient associated with the lower reaches of a river comes an increase in deposition, and this leads to the formation of wide floodplains and levees either side of the channel
What are the two types of river profiles?
Rivers can be described as having two distinct profiles: long profile and cross-valley profile. As geographers, we need to be able to describe and explain the form and structure of both.
What influences cross valley profiles?
Further influences on cross-valley profiles. The precise shape of a river valley is not just a function of energy and erosion. There are other factors which determine the shape and angle of the slopes which make up the valley sides.
What is a cross valley profile?
The cross-valley profile is the cross-section through the river valley at any given point along the long profile. It includes the top of one side of the valley, across the valley floor which contains the river, up to the top of the other side of the valley. It changes with distance downstream from a steep-sided, narrow valley near the source, ...
How does a river erode?
Essentially, a river erodes its way down through the landscape (vertical erosion) until it reaches base level ( usually the sea but sometimes an inland lake). The long profile is often portrayed as a smooth concave shape although in reality there are sometimes sharp drops in gradient due to differential geology or rejuvenation (how a river responds to changes in base level caused by sea level change). The profile may exhibit a stepped profile where there are breaks in slope where waterfalls may be present.
What is graded river?
Some define the graded river as one in which inputs and outputs are balanced in the long term. At any given point along a river’s profile, the slope angle may be sufficient to discharge water and load but not to cause additional erosion to occur. In this way, the river is in equilibrium.
What happens when the base level of a river falls?
Similarly, if base level falls as a result of sea level change, a river can become rejuvenated. This will cause a river to experience a renewal in gravitational potential energy which leads it to start eroding vertically once again (assuming a graded profile). This can lead to the formation of landforms such as knick point waterfalls and incised meanders.
What are the three things that occur in a river?
Erosion, transportation and deposition all occur in a river. Moving from the upper course to the lower course, the rates of erosion, transportation and deposition change.
What is a long profile?
A long profile is a line representing the river from its source (where it starts) to its mouth (where it meets the sea). It shows how the river changes over its course.
Why is the channel shallow?
The channel is shallow and narrow because there is not a lot of water in the channel. B – as the river flows into the middle course, there is some vertical erosion but more lateral erosion. The channel is wider and deeper as a result. C - in the lower course there is a lot less erosion, with only some lateral erosion.
Is the river's load large or small?
The river's load is large in the upper course, as it hasn't been broken down by erosion yet. Lower course - in the lower course, the land is a lot flatter. The river's load is fine sediment, as erosion has broken down the rocks.
How does a river change?
A river changes with increasing distance downstream from its source towards its mouth. It moves through its upper course, to its mid-course and finally into its lower course. Steep valley sides are typical of a river's upper course in upland areas. The valley here has steep sides and the valley bottom is narrow.
What are the three things that occur in a river?
Erosion, transportation and deposition all occur in a river. Moving from the upper course to the lower course, the rates of erosion, transportation and deposition change.
What is the main process that creates large floodplains and deltas?
The river's load is fine sediment, as erosion has broken down the rocks. The river channel is at its widest and deepest as it flows towards its mouth. Deposition is the main process in this part of the river, which creates large floodplains and deltas.
Why are valleys called V-shaped valleys?
The valley here has steep sides and the valley bottom is narrow. This is why valleys like this are called V-shaped valleys. Upper course - this is where the river starts and is usually an upland area. Slopes are steep - this can increase the velocity of the river after heavy rainfall, when discharge is high.
Why are slopes steep?
Slopes are steep - this can increase the velocity of the river after heavy rainfall, when discharge is high. The river channel is narrow and shallow here. The river's load is large in the upper course, as it hasn't been broken down by erosion yet. When discharge is high vertical erosion erodes the river bed and larger sediments are transported by ...
Is the river channel wider or deeper?
B – as the river flows into the middle course, there is some vertical erosion but more lateral erosion. The channel is wider and deeper as a result.
